15min:

HE WANG, P. L. GOULD AND W. C. STWALLEY, Department of Physics, University of Connecticut, Storrs, CT 06269.

We report the first observation of fragmentation spectra of the fine-structure predissociated long-range 1_g and 0_u⁺ state of ultracold (T - 350µK) ³⁹K₂ molecules. The 1_g state predissociates via the curve crossing at long range with the repulsive 0_g⁺ state. The 0_u⁺ state, however, predissociates predominantly through molecular fine-structure mixing at short range with the b³ _1u component. Our technique of fragmentation spectroscopy is a sensitive and selective tool for studies of ultracold photoassociation and fine-structure-changing collisions.